Posts Tagged ‘CO2’

That is the question I’ve been pondering earlier this year and which’ pontifications you can now read on Planet3.

The difference is mainly in the timescale: CO2 lasts a lot longer in the atmosphere than most of the other warming agents (e.g. black carbon, ozone, methane). This means that the temperature will decrease faster when the emission of shortlived compounds is decreased, as compared to that of a longlived compound such as CO2.

The other side of the coin is that for long term warming, the cumulative emissions of CO2 are dominant, even if in the short term changes in its emission are relatively ineffectual. Other important aspects in this discussion are health effects from air pollution (e.g. soot and ozone) and political practicability (gridlock in global climate negotiations).

So the question is: Are you more concerned about the short term or the long term effects of climate change? Which is a similar question that is often implicitly present in climate debates: Weighing the right of this generation to economic wellbeing (through cheap fossil energy) with the right of future generations to a pleasant planet to live on (through us not using too much cheap fossil energy). Strangely enough, that central and deeply ethical question is usually embodied in the discount rate (as used in economics when comparing investments with the expected rate of return).

My conclusion:

It’s clear that for long term climate stabilization, cumulative CO2 reductions are paramount, and that for the short term, reducing other forcings can offer faster results and offer other benefits as well. So the answer to the question “what should we focus on” is “all of the above”. I would applaud more attention to the non-CO2 forcings in the International policy arena. However, let’s not forget that there’s a hefty price and/or climate tag to pay in the end for delaying CO2 emission reductions.

Listen to Scott Denning’s sharp and to-the-point presentation, which he gave at Heartland’s climate conference, here. It’s worth the full 16 minutes of it. He rocks. Alternatively, read this little recap:

Denning attended the Heartland conference for the second year in a row and it seems like he’s outdone himself by giving an even better and sharper presentation than last years (which was excellent as well).

He emphasized some very important things:

– The big picture is what matters; details do not (at least in terms of policy relevance; for science nerds of course it’s different)

– Part of that big picture is that, whatever the sensitivity, a 400% increase in CO2 is going to make a big difference to the climate, because of the simple fact that adding heat warms things up.

– He offered a big challenge to the (strongly contrarian and libertarian) audience: Propose and advocate for effective solutions, otherwise others will. Policy will be enacted anyway. His challenge got particularly strong when he said “do you want Greenpeace to dictate the policy? (…) Are you cowards?”

This self-description of a lukewarmer (at Bishop Hill) gave me a good laugh:

Now I’m probably some sort of a lukewarmer – I don’t e.g. agree with Turning Tide that the fact that CO2 concentrations are low means ipso facto that it is irrelevant.

Like luketoxers who acknowledge the fact that arsenic in low concentrations doesn’t ipso facto mean that it’s irrelevant. It’s like saying I’m not a total doorknob.

Curious, I went back to read what Turning Tide had written and came across this gem:

What I found most telling is how certain facts about the atmosphere are very hard to track down for the layperson. For example, I’m pretty sure the average joe has no idea how little CO2 there is in the atmosphere, and how small a proportion of that little amount is contributed by human activities. It’s almost as though there’s a conspiracy of silence to keep such information out of easily accessible sources.

Can everyone who has a CO2 concentration widget on their blog please remove it now? We’ve got to keep it a secret that its concentration is a meagre 395 parts per million.

Like this:

Jeff Id took issue with Chris Colose for bringing up the high surface temperature at Venus in his SkS post:

CO2 is a strong greenhouse gas, and it is important in impeding how efficiently our planet loses radiative heat to space. We don’t often think of CO2 as a “pollutant” on Venus, yet it still allows the planet to support temperatures well above the melting point of lead or tin.

Venus does have a more reflective atmosphere but it is also closer to the sun than the Earth. For the thinking mind, it is difficult to ignore that the atmosphere is a ridiculous 90 times more dense. (…) In fact, if you just used Nitrogen alone at the same mass you would get a ton of heat just by the insulating properties of a gas.

My reply was that it was the pressure and amount of gas which caused the temperature more than the specific greenhouse effect of some particularly powerful gas. I pointed out that even N2 would cause a ton of warming with wording that clearly recognized there would be less warming and a paper was referenced where even the 96.5 percent N2 atmosphere had 80C of warming. I was also careful not to claim that all gasses would definitely cause a hot Venus and intentionally phrased even that as a question. In other words, you are making assumptions of a point I didn’t state.

To be fair, I admit that a pure nitrogen atmosphere had less warming than I would have (but did not) guess.

Is it just me, or does that indeed sound like he agrees that the majority of the >500 degrees greenhouse effect on Venus stems from the radiative properties of its atmosphere (~96% CO2) rather than from its density/pressure? The impression I got from his post was that the opposite though. Makes me wonder what the argument is really about. So I asked:

Jeff,

It seems that you agree that the high temperature on Venus is due primarily to a strong CO2 greenhouse effect (few hundred deg) and secondarily (?) to the high surface pressure (the ~80 deg number that was mentioned upthread).

If so, then I don’t understand the beef you have with Chris’ take, where he uses Venus as an example that shows that CO2 is a greenhouse gas.

I object to its comparison to Earth as a scare tactic in general. That’s all.

Argument resolved. Both agree that the greenhouse properties of Venus’ atmosphere are primarily responsible for its high surface temperature, and they disagree as to whether or how this could be mentioned in a discussion about Earth’s climate.

Quick rundown on Venus’ climate:

Venus is closer to the sun than the Earth, but its higher reflectivity more than compensates for that. Without a greenhouse effect Venus would actually be colder than the Earth would be without a greenhouse effect. In reality Venus is about 500 degrees warmer than this so called black body temperature (the greenhouse effect on the Earth is about 33 degrees). This is primarily due to the inception of infrared radiation by its thick atmosphere of almost pure CO2. The high density also helps, but is of secondary importance.

Several times in recent weeks people have commented that the sun is responsible for the current climate change rather than CO2. Ironically, this was sometimes argued by the same people who were cheering on the claim that there is no deterministic forcing at work in driving temperatures upwards (be it GHG or the sun or whatever else). So much for coherence.

Let’s look at how the global average temperature, CO2 and the sun changed over recent decades:

Temperatures jiggle up and down, but are increasing over the longer term (multiple decades). CO2 has a seasonal cycle due to the ‘breathing’ of the biosphere, but is steadily increasing over the years due to human emissions. The sun shows an 11-year cycle, but no secular increase or decrease over this time period.

Let’s go a bit farther back in time (HadCRU temperatures up to 2008; number of sunspots as a proxy of solar activity; original here):

And looking back at sunspot observations over the past 400 years (original):

So what does this tell us? Of course changes in the sun affect our climate (coherence check: This implies a certain degree of determinism). Low solar activity (e.g. during the Maunder and the Dalton minima) played a role in the so called ‘little ice age’. In the beginning of the 20th century solar activity increased, which contributed to the warming (together with greenhouse gases and a lack of volcanic activity). However, since the solar output (including cosmic rays) remained steady (or even decreased a bit) since the 1950’s, it doesn’t seem very likely that the sun contributed to the recent increase in temperatures since the 1970’s. The little ice age ended (~1850) long before the recent warming started (~1975), so no causal relation there either.

The main reasons that disqualify the sun as being a major culprit in recent global warming are:

• No increase in solar output (or decrease in cosmic rays) over the past 50 years

Below are two graphs of global average temperature and CO2 concentration. First I show the temperature anomaly from the three major datasets of surface temperature together with the CO2 concentration as measured at Mauna Loa since 1958:

The CO2 concentrations are plotted on a logarithmic axis because the temperature effect of CO2 is logarithmic. The 11 year running mean through the yearly temperature anomalies is given by the thick colored lines.

Before the 1970’s, the temperature trend was more or less flat for a few decades (see also the graphs in this earlier post). The strong increase in cooling aerosols (resulting from e.g. SO2 emissions) counteracted much of the greenhouse warming over that period. Since that time however, greenhouse forcing has been dominant, resulting in the temperature and CO2 trends following a similar pattern (at least over the multi-decadal timescale; short term variability is heavily influenced by e.g. El Nino/La Nina, major volcanic eruptions and other natural phenomena). A graph of the time evolution of relevant known climate forcings over the past 130 years can be found here.

A very popular graph that purportedly falsifies the whole “AGW dogma” is the following, showing unrelated trends of temperature and CO2 for a recent 11 year period. It’s been carefully crafted to create a certain impression:

– The graph purposefully starts at a record high temperature (1998) to maximize the visual impression of “falling temperatures”. It also strongly depends on the specific datasets used. This is a clear example of cherrypicking.

Using the same logic as this graph is based on, one could also falsify the theory of gravity by pointing to a bird in the sky (conveniently forgetting that there are more forces than gravity and that the bird has wings).